1. Thin-layer chromatography of porphyrin methyl esters provides a useful and rapid technique for resolving mixtures of porphyrins from biological samples.

2. Application of this technique to urinary, faecal and hepatic porphyrins from patients with symptomatic porphyria revealed five porphyrins of interest which could be identified by mass spectrometry as the methyl esters of porphyrins with 8-, 7-, 6-, 5- and 4-carboxyl groups. Millimolar extinction coefficients at the Soret absorption maxima for these porphyrin methyl esters in chloroform solution were measured.

3. A consistent pattern of urinary porphyrin excretion in symptomatic porphyria was seen with 8-, 7-, 6-, 5- and 4-carboxyl porphyrins constituting approximately 60%, 25%, 3%, 3% and 9% of the total respectively. Uroporphyrin (73%), hepta-carboxylic porphyrin (26%) and hexa-carboxylic porphyrin (1%) were the only porphyrins detected in the liver of one patient.

4. Isomer analysis of excreted and hepatic porphyrins revealed that uroporphyrin was approximately 35% isomer III, hepta- and hexa-carboxylic porphyrins almost all isomer III and penta-carboxylic and coproporphyrin approximately 50% isomer III.

5. To explain these findings it is suggested that there are two metabolic pathways for the handling of δ-aminolaevulic acid (ALA) in the liver.

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